Chromatography is a widely used technique for separating organic and inorganic compounds and substances, e.g., amino acids, proteins, nucleic acids, hydrocarbons, and carbohydrates. Effective chromatography is influenced mainly by efficiency and selectivity of a chromatographic medium with respect to specific compounds of interest. Major improvements in column efficiency can be obtained by using more uniform particle size, or in the case of high performance liquid chromatography (HPLC), decreasing particle size of the packing material. For example in the past years, typical particle size for HPLC has decreased from about ten micrometers (μm or micron) to 1.8 μm, yielding a great increase increased in column efficiency. However, reduction in particle size can be accompanied by higher operating pressures and a need for more sophisticated design and expensive instrumentation such as ultra-high pressure liquid chromatography (UHPLC) systems. See Skoog et al. 1997 Principles of Instrumental Analysis (fifth edition) Brooks Cole Publishing p. 725-743; and Skoog et al. 2006 Principles of Instrumental Analysis (sixth edition) Brooks Cole Publishing chapter 28.
A more effective approach for improving compound resolution is to alter the column selectivity of the chromatographic medium with respect to specific compounds. The packing material for liquid chromatography is commonly based on porous silica particles. The silanol functional groups on the silica surface can be modified by conjugating with a variety of alkyl and other functional groups to change the affinity and selectivity of the packing materials to different compounds. For example, attaching a C18 alkyl chain on the silanol group creates so called reversed-phase liquid chromatographic media that are widely used for separating polar organic compounds. Other ways of modifying the resolution properties of silica gel include physically attaching compounds or ions onto the surface of porous silica particles. For example, silver ion (Ag+) has been attached by a process referred to as impregnation onto the silica surface by immersing the silica gel in an aqueous solution of silver nitrate (AgNO3). The silver-imbedded silica gel is used to bind to molecules having electron rich bonds (Zeng et al., international application number PCT/US2011/046810 filed Aug. 5, 2011 which is incorporated by reference herein in its entirety).
While chromatographic media is effective for binding many molecules (e.g., proteins), it would be useful to have media that selectively bind metals or metal compounds. Media that specifically bind metal ions (e.g., silver, platinum, and nickel) and that bind metal-containing molecules are needed for medical, industrial and pharmaceutical applications. Palladium compounds are widely used catalysts for carbon-carbon and carbon-heteroatom coupling reactions (e.g., Heck, Suzuki-Miyaura, Stille, Negishi, and Tsuji-Trost reactions) and are commonly used in pharmaceutical development and production. For the synthesis of pharmaceutical compounds there are strict regulations that require the amount of heavy metals, such as palladium, to be limited to amounts of about two parts per million (ppm) to 20 ppm in the active pharmaceutical ingredient (Garrett, C. E. et al. 2004 Adv. Synth. Catal. 346: 889-900). There is a current need for improved materials and more efficient methods for scavenging, removing or separating metals for example in the synthesis and purification of active pharmaceutical ingredients.